Most of the previous studies of cardiac muscle mechanics have involved the use of the quick-release technique to measure the elasticity and viscosity of isolated cat papillary muscles. In order to make more precise measurements of both of these properties than is possible with the quick-release technique and to provide for the first time the ability to measure their changes continuously during a complete contraction cycle, I have developed a sinusoidal forcing technique for cat papillary muscle. In addition, a similar sinusoidal forcing technique has been developed which provides the first direct measurements of elasticity and viscosity in isovolumically-contracting left ventricles of dogs. The aims of the proposed investigation will be to study 1) the influence of changes in frequency of the sinusoidal forcing function on papillary muscle for the purpose of determining a multicomponent mechanical model consisting of either linear or nonlinear elastic, viscous, and inertial elements; 2) the influence of changes in resting length, extracellular calcium concentration, stimulation rate, norepinephrine infusion, hypo- and hyperthermia, and hyperosmolality on elastic and viscous stiffness, measured by the sinusoidal forcing technique; and 3) comparison of elastic and viscous measurements in papillary muscle with comparable measurements in the intact left ventricle.